1Department of
Biomedical Engineering, Yale University, New Haven, CT, USA; 2Department
of Diagnostic Radiology, Yale University School of Medicine, New Haven, CT,
USA

Inorganic manganese particles are attractive for
molecular and cellular imaging due to their potential to provide bright
contrast on MRI.We have fabricated
pH-sensitive, poly(lactic-co-glycolic-acid) (PLGA) encapsulated manganese
oxide (MnO) nanocrystals. Particles were fabricated at 140-nm and
1.7-μm, and incorporated 15 to 20-nm MnO nanocrystals. Intact particles
at physiological pH cause little MRI contrast, but following endocytosis into
low pH compartments within cells, particles erode, and MnO dissolves to
release Mn2+, causing cells to appear bright on MR images. The
change in MRI properties is as high as 35-fold, making it the most dynamic
smart MRI contrast agent yet reported.